1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a LCD device having a dynamic aperture ratio control system for controlling aperture ratio and brightness.
2. Discussion of the Related Art
A cathode ray tube (CRT) has been mainly used as displays for televisions and desktop computer monitors, but the CRT has disadvantages of heavy weight, large dimension and high power consumption. Therefore, flat panel display (FPD) devices have been demanded to substitute the CRT. For example, liquid crystal display (LCD) devices and electroluminescent display (ELD) devices have been researched and developed. Particularly, the LCD devices make use of optical anisotropy and polarization properties of liquid crystal molecules that are interposed between array substrate and color filter substrate
FIG. 1 is an expanded perspective view of a liquid crystal display device according to the related art. The LCD device includes an upper substrate 5 that is commonly referred to as a color filter substrate, a lower substrate 22 that is commonly referred to as an array substrate, and a liquid crystal material layer 14 that is interposed between the upper and lower substrates 5 and 22, respectively. A color filter layer 7 is formed in the shape of a matrix on the upper substrate 5, and a black matrix 6 is also formed on the upper substrate 5. The color filter layer 7 includes a plurality of red (R), green (G) and blue color filters 7a, 7b and 7c, which are surrounded by the black matrix 6. Additionally, a common electrode 18 is formed on the cover of the color filter layer 7 and the black matrix 6.
A plurality of thin film transistors T are formed on the lower substrate 22 in the shape of a matrix corresponding to the color filters 7a, 7b and 7c. A plurality of crossing gate lines 13 and data lines 15 are perpendicularly positioned such that each thin film transistor (TFT) T is located adjacent to each crossing of the gate lines 13 and the data lines 15. Furthermore, a pixel electrode 17 is formed on a sub-pixel region Ps defined by the gate lines 13 and the data lines 15 of the lower substrate 22. The pixel electrodes 17 are formed of a transparent conductive material (e.g., indium-tin-oxide; ITO) in a matrix type, and each pixel electrode 17 corresponds to each of the color filters 7a, 7b and 7c. The sub-pixel regions Ps are often referred to as dots, and are actually employed for displaying images with the corresponding color filters by the modulation of the liquid crystal layer 14.
A scanning signal is supplied to a gate electrode of the thin film transistor T through the gate line 13, and a data signal is supplied to a source electrode of the thin film transistor T through the data line 15. As a result, the liquid crystal molecules of the liquid crystal material layer 14 are aligned and re-arranged by enablement of the electric field between the common electrode 18 and the pixel electrodes 17. The liquid crystal molecules of the liquid crystal layer 14 have a spontaneous polarization property such that the liquid crystal arrangement changes in accordance with the electric field when voltages are applied to the pixel and common electrodes 17 and 18. The re-arrangement of the liquid crystal molecules acts as photo modulation that shuts and opens incident light passing through the liquid crystal layer 14, thereby displaying desired images. Further, the LCD device includes driving circuitries, wherein the circuitries control and change RGB data and other control signals originating from the driving system into desired signals in order to enable the liquid crystal panel to display the color images.
FIG. 2 is a schematic block diagram illustrating the liquid crystal display device according to the related art. In FIG. 2, a liquid crystal display (LCD) device 100 includes a liquid crystal (LC) panel 120 and a driving circuit 130. The LC panel 120 includes a plurality of gate lines 122 and a plurality of data line 124. The gate lines 122 perpendicularly cross the data lines 124 to define sub-pixel region Ps with the data lines 124. A switching element T, e.g., a thin film transistor, is disposed near a crossing of the gate and data lines 122 and 124 and connected to the gate and data lines 122 and 124. The driving circuit 130 normally receives RGB data and other control signals from a driving system (not shown), and then applies electric signals to the LC panel 120. The driving circuit 130 includes a timing controller 136, a gamma voltage generator 138, a gate driver 132 and a data driver 134. The gate driver 132 is connected to the plurality of gate lines 122 and supplies gate signals to the gate lines 122. The data driver 132 is connected to the plurality of data lines 124 and supplies data signals thereto.
In addition, the timing controller 136 transmits the RGB data and other control signals received from the driving system (not shown) to the data driver 134. The control signals are a plurality of timing synchronization signals that include a vertical synchronization signal as a frame identification, a horizontal synchronization signal as a line identification, an enable signal as a data input indicator, and a main clock. After receiving the timing synchronization signals, the timing controller 136 generates data control signals and gate control signals, respectively, and re-arranges the RGB data in accordance with the timing synchronization signals. Namely, the RGB digital data, a horizontal synchronization signals, a vertical line start signal for RGB digital data input, and source pulse clock for data shift are transferred to the data driver 134 from the timing controller 136. Furthermore, the timing controller 136 transmits a vertical synchronization signal, a vertical line start signal for gate-on-signal input, and a gate clock for sequential gate signal input into the gate driver 132. Additionally, the gamma voltage generator 138 generates an RGB reference voltage using the RGB data and transmits the RGB reference voltage to the data driver 134.
Meanwhile, when the LCD device displays moving images after displaying a still picture for a long time, some image patterns of the previous still picture remain occasionally, i.e., it is called as residual images. Especially, such residual images occur at the time of applying DC voltage between the common and pixel electrodes because the liquid crystal has refractive birefringence property and is easily deteriorated by the DC voltage. Therefore, the liquid crystal layer is generally driven and operated by an AC voltage. Further, if the polarity of voltage applied to the pixel and common electrodes is fixed, the liquid crystal deterioration is further increased, whereby the applied voltage polarity may be converted for each frame with respect to the driving method. Specifically, one of a field inversion driving method, a line inversion driving method and a dot inversion driving method may be employed for converting the applied voltage polarity.
In the field inversion method, the data signal supplied to the LC panel is inverted whenever the field is changed. In the line inversion method, the data signal is inverted in accordance with the gate line of the LC panel. Further, in the dot inversion method, the data signal polarity of one pixel is opposite to that of adjacent pixels, and the data signal applied to the LC panel is inverted in each field. When adopting such inversion methods to the LCD device, the driving circuitry 130 of FIG. 2 may include a polarity applier (not shown). Among the inversion methods mentioned above, the dot inversion method is widely used because the dot inversion method most frequently changes the polarity.
Referring back to FIG. 1, the sub-pixel regions Ps correspond to the R, G and B color filters 7a, 7b and 7c, and the set of R, G and B color filters 7a, 7b and 7c form a pixel that represents a desired color by mixing the red (R), green (G) and blue (B) colors so as to display an image. If the LCD device of FIG. 1 adopts the dot inversion method, each sub-pixel has a polarity different from its neighboring pixels. Namely, the data signal is inverted for each of the R, G and B colors. At this point, the color filters 7a, 7b and 7c corresponding to the sub-pixel regions Ps are proposed to have the following arrangements.
FIGS. 3-7 are plan views illustrating arrangements of sub-pixels: a stripe type, a mosaic type, a triangle type, a square type, and a quad type.
FIG. 3 shows a stripe type arrangement of color filters. In FIG. 3, the sub-pixel regions Ps line up uniformly in rows and columns. The red (R), green (G) and blue (B) color filters are alternately arranged in a row direction, but the same color filters, red (R), green (G) or blue (B), are also arranged in a column direction.
FIG. 4 shows a mosaic type arrangement of color filters. In FIG. 4, the sub-pixel regions Ps line up uniformly in rows and columns. However, unlike the stripe type arrangement of FIG. 3, the red (R), green (G) and blue (B) color filters are alternately arranged in both the row and column directions.
FIG. 5 shows a triangle type arrangement of color filters. In FIG. 5, the sub-pixel regions Ps line up in row, but the sub-pixels disposed in a column make a diagonal loop shape. The red (R), green (G) and blue (B) color filters are alternately arranged in the row direction. However, in the column direction, the red (R), green (G) and blue (B) color filters are arranged so as not to have the same colored filters attached together. Namely, if the red (R) and green (G) color filters are arranged to be attached to each other in a first row, the blue (B) color filter is positioned in an area between the red (R) and green (G) color filter in a second row. In this manner, the red (R) color filter of the second row is positioned in an area between the green (G) and blue (B) color filters of the first row, and the green (G) color filter of the second row is positioned in an area between the blue (B) and red (R) color filters of the first row. Therefore, the red (R) and green (G) color filters of the first row and the blue (B) color filter of the second row form a triangle shape. Hence the reason why the arrangement of FIG. 5 is called the triangle type.
FIG. 6 shows a square type arrangement of color filters. In FIG. 6, the sub-pixel regions Ps are drawn up uniformly in rows and columns. The red (R), green (G) and blue (B) color filters are alternately arranged in the row direction, but only two colored filters are alternately arranged in the column direction. For example, the red (R) and green (B), green (G) and blue (B), or blue (B) and red (R) color filters are alternately arranged along the column direction without the other colored filter.
FIG. 7 shows a quad type arrangement of color filters. In FIG. 7, white (W) color filters are included with the red (R), green (G) and blue (B) color filters. The sub-pixel regions Ps stand uniformly in rows and columns. The red (R), green (G), blue (B) and white (W) color filters are gathered together to form a larger rectangular shape. Namely, two of the red (R), green (G), blue (B) and white (W) color filters are alternately arranged in a first row, and the other two color filters are alternately arranged in a second row. Due to the fact that the white (W) color filter is additionally formed, the LCD device having the quad type arrangement of color filters can have improved brightness, high aperture ratio, and better contrast ratio. Further, the sub-pixel having the white (W) color filter may be operated by an additional data signal.
Meanwhile, the white (W) sub-pixels may not have any colored filters because a light source employed in the LCD device usually emits white-colored light.
Among the above-mentioned color filter arrangements, the stripe type, mosaic type, triangle type and square type arrangements provide relatively low brightness, and have the disadvantages of the invariable and stationary aperture and contrast ratios. Furthermore, although the high brightness and improved aperture and contrast ratios are obtained, the LCD device having the quad type arrangement needs a complicated circuit and requires the high costs of production because an additional data signal is required for the white (W) sub-pixel. Further, the LCD device having the red (R), green (G) and blue (B) color filters may have a narrower color gamut because only three colors, red, green and blue colors, are employed to display desired color images.